Alkylation catalyst and method for making alkylated phenols

ABSTRACT

An alkylation catalyst comprises a metal oxide wherein the catalyst has a surface area to volume ratio of about 950 m 2 /m 3  to about 4000 m 2 /m 3 .

BACKGROUND OF INVENTION

This disclosure relates to alkylation catalysts and in particular toalkylation catalysts containing magnesium oxide or iron oxide, theirmethods of preparation and use in alkylation reactions.

Ortho-alkylated hydroxy aromatic compounds are useful for a variety ofpurposes. For example, ortho-cresol is a useful disinfectant and woodpreservative. It is often prepared by the vapor-phase reaction of aphenol with methanol. In another alkylation reaction, ortho-cresol andphenol can both be converted into 2,6-xylenol. This xylenol monomer canbe polymerized to form poly(2,6-dimethyl-1,4-phenylene)ether, which isthe primary component in certain high-performance thermoplasticproducts.

Alkylated hydroxy aromatic compounds are usually prepared by thealkylation of the precursor hydroxy aromatic compound with a primary orsecondary alcohol. The alkylation must be carried out in the presence ofa suitable catalyst, such as a magnesium-based or iron-based compound.

A great deal of attention has been paid to optimizing the performance ofmagnesium-based catalysts in an industrial setting. Usually, it is veryimportant for the catalyst to have high activity, i.e., it must have aslong of an active life as possible. Moreover, the catalyst must havevery good ortho-selectivity. Many of the ortho-alkylation catalysts usedin the past produced a high proportion of para-alkylated products ofmarginal utility.

As an illustration, the alkylation of phenol with methanol in thepresence of a magnesium oxide catalyst yields ortho-cresol (o-cresol)and 2,6-xylenol, which are desirable products. However, the alkylationreaction may also produce substantial amounts of para-substitutedcompounds, such as para-cresol (p-cresol), 2,4-xylenol, and mesitol(2,4,6-trimethylphenol). In some end use applications, thesepara-substituted compounds are much less useful than the correspondingcompounds containing unsubstituted para positions.

While improvements in selectivity, activity and catalyst life have beenmade, there is an ongoing need for improved selectivity, activity andcatalyst life in order to improve the efficiency of the alkylationprocess.

SUMMARY OF INVENTION

An alkylation catalyst comprising a metal oxide wherein the catalyst hasa surface area to volume ratio of about 950 m²/m³ to about 4000 m^(2/)m³and/or an aspect ratio of about 0.7 to about 1.0.

An alkylation method comprising reacting a hydroxy aromatic compoundwith an alkyl alcohol in the presence of an alkylation catalystcomprising a metal oxide wherein the alkylation catalyst has a surfacearea to volume ratio of about 950 m²/m³ to about 4000 m²/m³ and/or anaspect ratio of about 0.7 to about 1.0.

DETAILED DESCRIPTION

Alkylated hydroxy aromatic compounds are manufactured by vapor phasereaction of an alkyl alcohol and hydroxy aromatic compound in thepresence of an alkylation catalyst. It has been unexpectedly discoveredthat employing a catalyst having a surface area to volume ratio of about950 to about 4000 m²/m³ and/or an aspect ratio of about 0.7 to about 1.0improves the selectivity of the reaction. The surface area to volumeratio and/or aspect ratio increases the unpacked bulk density of thecatalyst. The increase in unpacked bulk density results in an increasein the amount of catalyst that can be loaded into the reactor whichsurprisingly does not have a negative impact on selectivity andproductivity and increases the time between catalyst change-outs thusincreasing overall efficiency.

Pellet is defined herein as a small, densely packed mass of catalystwith no restriction with regard to geometry. Unpacked bulk density isdefined herein as the density of randomly arranged pellets in a givenvolume. This is in contrast to a packed bulk density, which can bedefined as the density of non-randomly arranged pellets in a givenvolume. Both of these are in contrast to pellet density, which is theaverage density of each pellet (weight per unit volume).

Hydroxy aromatic compounds include aromatic compounds having at leastone hydroxy functional group and 6 to about 20 carbons. The hydroxyaromatic compound may comprise one aromatic ring or multiple aromaticrings that may be fused or unfused. The hydroxy aromatic compound hasone or more ortho hydrogens. Additionally, the hydroxy aromatic compoundmay be substituted at the meta- and/or para- positions relative to thehydroxy functional group. Preferred hydroxy aromatic compounds includephenol and o-cresol.

Alkyl alcohols include saturated and unsaturated alkyl alcohols havingone to about ten carbons. The alkyl alcohol may be branched orunbranched, primary or secondary. Specific examples of the alkyl alcoholinclude methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propylalcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, and thelike, as well as combinations comprising at least one of the abovementioned alkyl alcohols. A preferred alkyl alcohol is methyl alcohol(methanol).

The alkylation catalyst comprises, as a main constituent, at least onemetal oxide. The metal oxide can be obtained from a metal oxideprecursor comprising a magnesium reagent, an iron reagent or a mixtureof the foregoing. Any magnesium reagent which yields magnesium oxide canbe used. Likewise, any iron reagent which yields iron oxide can be used.Preferred magnesium reagents include, but are not limited to, magnesiumoxide, magnesium hydroxide, magnesium carbonate, magnesium nitrate,magnesium sulfate, magnesium carbonate, basic magnesium carbonate,magnesium acetate, and mixtures of the foregoing. The magnesium reagentis typically in the form of a powder. Basic magnesium carbonate is apreferred magnesium reagent. Basic magnesium carbonate is sometimesreferred to as “magnesium carbonate hydroxide”. Those skilled in the artunderstand that the exact formula for basic magnesium carbonate variesto some extent.

Examples of iron reagents used for the preparation of the catalystinclude, but are not limited to, ferric nitrate, ferric sulfate, ferricchloride, ferrous nitrate, ferrous sulfate and ferrous chloride. Ofthese, ferric nitrate is particularly preferred. Furthermore, the ironoxides can be in any form of FeO, Fe₂O₃, Fe₃O₄, or mixtures of theforegoing.

In one embodiment, the level of chlorides in the magnesium reagent isless than about 250 parts per million (ppm), preferably less than about125 ppm, and more preferably less than about 100 ppm. (As used herein,“chlorides” refers to chloride ions, which are often present in the formof a salt). The level of calcium in the magnesium reagent should be lessthan about 2500 ppm, and preferably, less than about 1000 ppm. In someembodiments, the level of calcium is less than about 750 ppm. (Theselevels of impurities can alternatively be specified with respect to themagnesium oxide-form which results from calcination. The impuritythreshold levels in the calcined oxide would be approximately twicethose for a basic magnesium carbonate reagent, e.g., less than about 500ppm chlorides and less than about 5000 ppm calcium, in the broadestembodiment).

The levels of chlorides and calcium in the magnesium reagent can bedetermined by common analytical methods. For example, calcium levels canbe determined by a titration technique or by some form of spectroscopy,e.g., inductively coupled plasma atomic emissions spectroscopy. Chloridelevels are usually determined by titration or by ion chromatography.Magnesium reagents of this type can be made available by commercialsources upon request.

The alkylation catalyst is formed by dry-blending the metal oxideprecursor with at least one filler and an optional pore former. The term“filler” is meant to encompass various lubricants, binders and fillersthat are known in the art for incorporation into this type of catalyst.The total amount of filler present in the catalyst composition isusually up to about 20% by weight, based on the total weight of fillerand magnesium reagent. In some embodiments, the level of filler is up toabout 10% by weight. Examples of fillers used in the catalystcomposition include graphite and polyphenylene ether (PPE). Thepolyphenylene ether is usually used in an amount of up to about 10% byweight, based on total weight, while the graphite is usually employed inan amount of up to about 5% by weight.

The optional pore former is a substance capable of aiding the formationof pores in the catalyst and is preferably selected from the groupconsisting of waxes and polysaccharides. The waxes can be selected fromone or more of paraffin wax, polyethylene wax, microcrystalline wax,montan wax, and the like. The polysaccharide may be selected from one ormore of cellulose, carboxyl methyl cellulose, cellulose acetate, starch,walnut powder, citric acid, polyethylene glycol, oxalic acid, stearicacid and the like. Also useful are anionic and cationic surfactants,typically long chain (C₁₀₋₂₈) hydrocarbons containing neutralized acidspecies, e.g., carboxylic acid, phosphoric acid, and sulfonic acidspecies.

The amount of the pore former is that amount which provides for adistribution of pore diameters of about 100 to about 400 Angstroms aftercalcination and typically ranges between about 100 ppm to 10 wt %,usually between about 100 ppm and 5 wt %, and preferably in amounts upto about 2 wt %, based on the total weight of metal oxide precursor,filler and pore former. In some embodiments the alkylation catalyst willhave a bimodal distribution of pores. It is believed that the first andsmaller diameter pore distribution is obtained from the metal oxideprecursor during the calcination process, i.e. these pores are ofsimilar dimension to those obtained from calcination of the metal oxideprecursor not containing the pore former. The second and larger diameterpore distribution is believed to be the result of the addition andcalcination of the pore former reagent itself, i.e. these pore diameterswould not be found in substantial quantities after calcination of ametal oxide precursor not containing the pore former. Preferably, thebimodal distribution of pores has a first distribution of pores whereinthe first distribution has an average pore diameter less than 100angstroms and a second distribution of pores wherein the seconddistribution has an average diameter greater than 100 angstroms and lessthan 400 Angstroms.

As used in this disclosure, the term “dry blending” refers to thegeneral technique in which the individual ingredients are initiallymixed together in the dry state, without resorting to any “wet”techniques, such as suspension blending or precipitation. Any type ofmechanical mixer or blender can be used, such as a ribbon blender. Thoseskilled in the art are familiar with the general parameters fordry-blending this type of material. The ingredients should be mixeduntil an intimate blend is obtained, with the filler and optional poreformer being well-dispersed. The blending time is typically in the rangeof about 10 minutes to about 2 hours, at a shaft speed of about 5rotations per minute (rpm) to about 60 rpm.

After dry-blending of the metal oxide precursor, filler (or multiplefillers) and optional pore former is complete, the blended, solidcatalyst composition is in the form of a powder. The powder usually hasa bulk density in the range of about 0.1 grams per cubic centimeter(g/cm³) to about 0.5 g/cm³, and preferably in the range of about 0.25g/cm³ to about 0.5 g/cm³. The powder then typically undergoes furtherprocessing, prior to being shaped into a desired form. Non-limitingexamples of the additional processing steps include sieving (to obtain amore narrow particle distribution), milling, and compressing.

In some preferred embodiments, the catalyst composition is compactedafter dry-blending. Compacting equipment is known in the art. Commercialcompacting systems are available from various sources, such asAllis-Chalmers; Gerteis Macshinen, Jona, Switzerland; and FitzpatrickCo., Elmhurst, Ill. The compactors usually function by feeding thepowdered material through rollers.

One specific example of a suitable compactor unit is known as the“Chilsonator”™. In such a system, the catalyst powder is first fed tocompaction rolls by a rapidly-turning vertical feed screw. The feedscrew forces the powder into a roll nip. The rolls compress the materialinto a continuous solid sheet.

In most embodiments, the catalyst composition is deaerated afterdry-blending, and prior to additional processing. This step isespecially important in those instances in which the composition mustsubsequently pass through compaction rollers. Deaeration furtherincreases the bulk density of the material by forcibly removingentrained gas (primarily air) from within the powder. Deaeration systemsare known in the art and available from various sources. Vacuumdeaeration is one common technique. The vacuum can be applied at variouspoints along the passage of the powder from the blending unit to otherprocessing operations. Usually, the vacuum is applied at a point veryclose to (and preceding) the location of compaction rollers. Thestrength of the vacuum will depend on various factors, such as theamount of powder being processed; its compressibility; the type offillers contained therein, and the density of the powder. Usually, thevacuum strength is in the range of about 5 inches (12.7 cm) mercury toabout 25 inches (63.5 cm) mercury.

The solid sheets of catalyst material formed by compaction may then begranulated by various techniques. The granulated material is typicallysize-separated. The desired catalyst granules can then be conveyedimmediately to a shaping operation, or to a storage facility. The shapeof the catalyst is not critical for this invention and will depend onthe manner in which the catalyst is being used for subsequent alkylationoperations. Very often, the catalyst is compressed into a pellet or“tablet”. Conventional pelletizing equipment can accomplish this task(e.g., a Betapress), as described in U.S. Pat. No. 4,900,708. The shapedcatalyst composition is then calcined. Calcination is usually carriedout by heating the catalyst at a temperature sufficient to convert themetal oxide precursor to metal oxide, which is the active species in thecatalyst. Calcination increases the surface area of the catalyst. Thecalcination temperature may vary somewhat, but is usually in the rangeof about 350° C. to about 550° C. The calcination atmosphere may beoxidizing, inert, or reducing. Alternatively, the catalyst can becalcined at the beginning of the alkylation reaction. In other words,calcination can take place in the presence of the alkylation feedmaterials, i.e., the hydroxy aromatic compound and the alkyl alcohol.

The surface area of the catalyst pellets is about 100 square meters pergram (m²/g) to about 300 m²/g, based on BET analysis. The uncalcinedpellets have pellet density of about 1.3 g/cm³ to about 2.1 g/cm³.Within this range the pellets have a pellet density of greater than orequal to about 1.4 g/cm³, preferably greater than or equal to about 1.6g/cm³. Also within this range the pellets have a pellet density of lessthan or equal to about 2.0 g/cm³, preferably less than or equal to about1.9 g/cm³. It is known that with pellets having a surface area to volumeratio of less than about 950 m²/m³ the selectivity of the reactiondecreases when pellet density increases above about 1.6 g/cm³.Surprisingly, pellets having a surface area to volume ratio of greaterthan about 950 m²/m³ can have pellet densities greater than or equal toabout 1.6 g/cm³ without a negative impact on reaction selectivity.

In one embodiment, the catalyst pellets have a surface area to volumeratio of about 950 m²/m³ to about 4000 m²/m³. Within this range, thecatalyst pellets preferably have a surface area to volume ratio greaterthan or equal to about 1100 m²/m³ and more preferably greater than orequal to about 1300 m²/m³. Also within this range the catalyst pelletshave a surface area to volume ratio less than or equal to about 3800m²/m³ and more preferably less than or equal to about 3000 m²/m³.

In another embodiment, the catalyst pellets have an aspect ratio ofabout 0.7 to about 1.0. Within this range, the aspect ratio ispreferably greater than or equal to about 0.72 and more preferablygreater than or equal to about 0.75. Also within this range, the aspectratio is preferably less than or equal to about 0.95 and more preferablyless than or equal to about 0.90. Aspect ratio is herein defined as theratio of length to diameter or length to width.

The catalyst pellets have an unpacked bulk density of about 900 to about1200 kilograms per cubic meter (kg/m³). Within this range, the unpackedbulk density is preferably greater than or equal to about 920, morepreferably greater than or equal to about 950 kg/m³. Also within thisrange, the unpacked bulk density is preferably less than or equal toabout 1180, more preferably less than or equal to about 1150 kg/m³.

In one embodiment, the catalyst pellets have a diameter of about 1.0 toabout 4.0 millimeters, and a height of about 2.0 to about 3.0millimeters.

The alkyated hydroxy aromatic compound is formed by reacting a hydroxyaromatic compound with an alkyl alcohol in the presence of an alkylationcatalyst comprising a metal oxide wherein the alkylation catalyst has asurface area to volume ratio of about 950 m²/m³ to about 4000 m²/m³, anaspect ratio of about 0.7 to about 1.0 or a combination of theforegoing. The temperature of the re-action is at least about 420° C.,and preferably is about 440° C. to about 500° C. The alkylation reactionmay be carried out in the presence of water vapor. The quantity of watervapor may be about 1 to about 35 weight percent (wt %), based on thetotal weight of the reactants, but is preferably about 5 to 25 wt %,based upon the total weight of the reactants.

In order to obtain a yield of ortho-alkylated products, at least onemole of the alcohol and preferably from 1 to 3 moles of the alcohol areused for each ortho-position on the phenol to be alkylated. For example,if phenol which has 2-ortho-hydrogens per molecule is to be methylatedto produce a yield of 2,6-xylenol, it is desirable to use two to sixmoles of methanol for each mole of phenol, with higher yields andselectivities being obtained with the higher ratio of methanol tophenol.

The alkylation reaction is generally carried out in a reactor systemwell described in the state of the art. The vapors issuing from thereactor are condensed and the product is separated by conventionalmethods such as crystallization, distillation, etc. The reactionproceeds at atmospheric pressure, but pressures above or below may alsobe used.

The alkylation techniques are generally known in the art, and describedin the above-referenced U.S. Pat. Nos. 4,554,267 and 3,446,856. Suitableprocesses are also described in U.S. Pat. Nos. 4,933,509; 4,900,708;4,554,266; 4,547,480; 4,048,239; 4,041,085; and 3,974,229.

Specific examples of alkylated aromatic hydroxy compounds include, butare not limited to, o-, m- and p-cresols; 2,3-, 2,4-, 2,5-, 3,4- and3,5-xylenols; trimethylphenols; tetramethylphenols; n- andiso-propylphenols; n-, iso- and tert-butylphenols; and the like, as wellas combinations and reaction products comprising at least one of theabove mentioned alkylated aromatic hydroxy compounds. In addition,alkylated aromatic hydroxy compounds include aromatic compounds havingat least two different alkyl substituent groups on the same aromaticring are also usable.

Having described the invention in detail, the following examples areprovided. The examples should not be considered as limiting the scope ofthe invention, but merely as illustrative and representative of makingalkylated phenols.

EXAMPLES

Alkylation catalysts comprising magnesium oxide were formed into pelletshaving two different sizes and calcined at 404° C. for 16 hrs undernitrogen flow at a WHSV of 0.12 g/g/hr. The pellet size of the calcinedpellets used in the first example was 2.96 millimeters in diameter and2.32 millimeters in height and the pellet size of the calcined pelletused in the second example was 4.45 millimeters in diameter and 2.95millimeters in height. The pellets in the first example had an aspectratio of 0.78 and a surface area to volume ratio of 1400 m²/m³. Thepellets in the second example had an aspect ratio of 0.66 and a surfacearea to volume ratio of 900 m²/m³. The catalysts were loaded into a labscale reactor for use in an alkylation reaction. The alklyation reactionemployed a feed comprising methanol and phenol in a weight ratio of 1.4.The feed also contained 20% water by weight. The reaction temperaturewas about 440° C. and the pressure was 170 kPa. The WHSV during reactionwas 2.1 g/g/hr.

Table 1 below summarizes the reaction selectivity, phenol usage andmethanol usage obtained after more than 150 hours runtime. Selectivityis defined as (Effluent moles (p-cresol+2,4-xylenol+mesitol))/(Effluentmoles (phenol+o-cresol+2,6-xylenol))×100. Phenol usage is defined as(phenol used/2,6 xylenol produced)×100. Methanol usage is defined as(methanol used/2,6 xylenol produced)×100.

TABLE 1 Methanol Reaction time Selectivity Phenol Usage Usage in hoursEx. 1 Ex. 2* Ex. 1 Ex. 2* Ex. 1 Ex. 2* 167 0.026 0.029 78.92 79.23 60.8861.67 173 0.025 0.029 78.85 79.21 60.96 61.72 191 0.023 0.027 78.7779.14 60.79 61.75 *Comparative Example

Results in the above tables clearly shows the increased selectivity ofthe pellets having a 1400 m²/m³ surface area to volume ratio and a 0.78aspect ratio over pellets having a 900 m²/m³ surface area to volumeratio and a 0.66 aspect ratio, and the strongly reduced phenol andmethanol usage for the production of 2,6 xylenol.

Table 42 shows the unpacked bulk density (UPBD) determined for thepellets described above.

UPBD in 45 millimeter tube (kg/m³) Example 1 Example 2* 1,063 802*Comparative example

Results in above table clearly show the increased unpacked bulk densityof the pellets having a 1400 m²/m³ surface area to volume ratio and a0.78 aspect ratio over pellets having a 900 m²/m³ surface area to volumeratio and a 0.66 aspect ratio. The increases in the unpacked bulkdensity increase the amount of catalyst that can be loaded in thereactor compared to earlier catalysts. The increase in loading resultsin decreased catalyst material usage and a longer reactor cycle time,making the method more efficient.

All patents cited herein are incorporated by reference.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theinvention scope thereof. It is, therefore intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of appendedclaims.

1. An alkylation catalyst comprising a metal oxide wherein the catalysthas a surface area to volume ratio of about 950 m²/m³ to about 4,000m²/m³ and further wherein the catalyst has a bimodal distribution ofpores.
 2. The catalyst of claim 1, wherein the metal oxide comprisesmagnesium oxide, iron oxide or a combination of the foregoing.
 3. Thecatalyst of claim 1, wherein the catalyst further comprises filler. 4.The catalyst of claim 1, wherein the catalyst has pores with diametersof about 100 to about 400 Angstroms after calcination.
 5. The catalystof claim 1, wherein the catalyst is in the form of pellets having asurface area of about 100 square meters per gram to about 300 squaremeters per gram.
 6. The catalyst of claim 1, wherein the uncalcinedcatalyst is in the form of pellets having a pellet density of about 1.30to about 2.10 grams per cubic centimeter.
 7. The catalyst of claim 1having a surface areas to volume ratio of about 1100 to about 3800m²/m³.
 8. The catalyst of claim 1, wherein the catalyst has an unpackedbulk density of about 900 to about 1200 kilograms per cubic meter. 9.The catalyst of claim 1, wherein the catalyst is in the form of pelletshaving a diameter of about 1.0 to about 4.0 millimeters and a height ofabout 2.0 to about 3.0 millimeters.
 10. An alkylation catalystcomprising a metal oxide wherein the catalyst has an aspect ratio ofabout 0.7 to about 1.0; and further wherein the catalyst has a bimodaldistribution of pores; and further wherein the catalyst is in the formof pellets having a pellet density of about 1.3 to about 2.10 grams percubic centimeter.
 11. The catalyst of claim 10, wherein the metal oxidecomprises magnesium oxide, iron oxide or a combination of the foregoing.12. The catalyst of claim 10, wherein the catalyst further comprises afiller.
 13. The catalyst of claim 10, wherein the catalyst has pareswith diameters of about 100 to about 400 Angstroms after calcinations.14. The catalyst of claim 10, wherein the catalyst is in the form ofpellets having a surface area of about 100 square meters per gram toabout 300 square meters per gram.
 15. The catalyst of claim 10, having asurface area to volume ratio of about 950 to about 4000 m²/m³.
 16. Thecatalyst of claim 10, wherein the catalyst has an unpacked bulk densityof about 900 to about 1200 kilograms per cubic meter.
 17. The catalystof claim 10, wherein the catalyst is in the form of pellets having adiameter of about 1.0 to about 4.0 millimeters and a height of about 2.0to about 3.0 millimeters.
 18. An alkylation catalyst comprising a metaloxide wherein the catalyst is in the form of pellets having a diameterof about 1.0 to about 4.0 millimeters and a height of about 2.0 to about3.0 millimeters and further wherein the catalyst has a bimodaldistribution of pores.
 19. The catalyst of claim 18, wherein the metaloxide comprises magnesium oxide, iron oxide or a combination of theforegoing.
 20. The catalyst of claim 18, wherein the catalyst furthercomprises filler.
 21. The catalyst of claim 18, wherein the catalyst haspores with diameters of about 100 to about 400 Angstroms aftercalcination.
 22. The catalyst of claim 18, wherein the catalyst has anunpacked bulk density of about 900 to about 1200 kilograms per cubicmeter.